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Journal Cover Physica D: Nonlinear Phenomena
  [SJR: 1.049]   [H-I: 102]   [3 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0167-2789
   Published by Elsevier Homepage  [3031 journals]
  • Wave turbulence theory of elastic plates
    • Authors: Gustavo Düring; Christophe Josserand; Sergio Rica
      Pages: 42 - 73
      Abstract: Publication date: 15 May 2017
      Source:Physica D: Nonlinear Phenomena, Volume 347
      Author(s): Gustavo Düring, Christophe Josserand, Sergio Rica
      This article presents the complete study of the long-time evolution of random waves of a vibrating thin elastic plate in the limit of small plate deformation so that modes of oscillations interact weakly. According to the wave turbulence theory a nonlinear wave system evolves in longtime creating a slow redistribution of the spectral energy from one mode to another. We derive step by step, following the method of cumulants expansion and multiscale asymptotic perturbations, the kinetic equation for the second order cumulants as well as the second and fourth order renormalization of the dispersion relation of the waves. We characterize the non-equilibrium evolution to an equilibrium wave spectrum, which happens to be the well known Rayleigh–Jeans distribution. Moreover we show the existence of an energy cascade, often called the Kolmogorov–Zakharov spectrum, which happens to be not simply a power law, but a logarithmic correction to the Rayleigh–Jeans distribution. We perform numerical simulations confirming these scenarii, namely the equilibrium relaxation for closed systems and the existence of an energy cascade wave spectrum. Both show a good agreement between theoretical predictions and numerics. We show also some other relevant features of vibrating elastic plates, such as the existence of a self-similar wave action inverse cascade which happens to blow-up in finite time. We discuss the mechanism of the wave breakdown phenomena in elastic plates as well as the limit of strong turbulence which arises as the thickness of the plate vanishes. Finally, we discuss the role of dissipation and the connection with experiments, and the generalization of the wave turbulence theory to elastic shells.

      PubDate: 2017-03-28T02:42:26Z
      DOI: 10.1016/j.physd.2017.01.002
      Issue No: Vol. 347 (2017)
       
  • A numerical estimate of the regularity of a family of Strange Non-Chaotic
           Attractors
    • Authors: Lluís Alsedà i Soler; Josep Maria Mondelo González; David Romero i Sànchez
      Pages: 74 - 89
      Abstract: Publication date: 15 May 2017
      Source:Physica D: Nonlinear Phenomena, Volume 347
      Author(s): Lluís Alsedà i Soler, Josep Maria Mondelo González, David Romero i Sànchez
      We estimate numerically the regularities of a family of Strange Non-Chaotic Attractors related with one of the models studied in (Grebogi et al., 1984) (see also Keller, 1996). To estimate these regularities we use wavelet analysis in the spirit of de la Llave and Petrov (2002) together with some ad-hoc techniques that we develop to overcome the theoretical difficulties that arise in the application of the method to the particular family that we consider. These difficulties are mainly due to the facts that we do not have an explicit formula for the attractor and it is discontinuous almost everywhere for some values of the parameters. Concretely we propose an algorithm based on the Fast Wavelet Transform. Also a quality check of the wavelet coefficients and regularity estimates is done.

      PubDate: 2017-03-28T02:42:26Z
      DOI: 10.1016/j.physd.2016.12.006
      Issue No: Vol. 347 (2017)
       
  • Full analysis of small hypercycles with short-circuits in prebiotic
           evolution
    • Authors: Josep Sardanyés; J. Tomás Lázaro; Antoni Guillamon; Ernest Fontich
      Pages: 90 - 108
      Abstract: Publication date: 15 May 2017
      Source:Physica D: Nonlinear Phenomena, Volume 347
      Author(s): Josep Sardanyés, J. Tomás Lázaro, Antoni Guillamon, Ernest Fontich
      It is known that hypercycles are sensitive to the so-called parasites and short-circuits. While the impact of parasites has been widely investigated for well-mixed and spatial hypercycles, the effect of short-circuits in hypercycles remains poorly understood. In this article we analyze the mean field and spatial dynamics of two small, asymmetric hypercycles with short-circuits. Specifically, we analyze a two-member hypercycle where one of the species contains an auto-catalytic loop, as the simplest hypercycle with a short-circuit. Then, we extend this system by adding another species that closes a three-member hypercycle while keeping the auto-catalytic short-circuit and the two-member cycle. The mean field model allows us to discard the presence of stable or unstable periodic orbits for both systems. We characterize the bifurcations and transitions involved in the dominance of the short-circuits i.e., in the reduction of the hypercycles’ size. The spatial simulations reveal a random-like and mixed distribution of the replicators in the all-species coexistence, ruling out the presence of large-scale spatial patterns such as spirals or spots typical of larger, oscillating hypercycles. A Monte Carlo sampling of the parameter space for the well-mixed and the spatial models reveals that the probability of finding stable hypercycles with short-circuits drastically diminishes from the two-member to the three-member system, especially at growing degradation rates of the replicators. These findings pose a big constraint in the increase of hypercycle’s size and complexity under the presence of inner cycles, suggesting the importance of a rapid growth of hypercycles able to generate spatial structures (e.g., rotating spirals) prior to the emergence of inner cycles. Our results can also be useful for the future design and implementation of synthetic cooperative systems containing catalytic short-circuits.

      PubDate: 2017-03-28T02:42:26Z
      DOI: 10.1016/j.physd.2016.12.004
      Issue No: Vol. 347 (2017)
       
  • A non-perturbative analytic expression of signal amplification factor in
           stochastic resonance
    • Authors: Asish Kumar Dhara
      Pages: 1 - 44
      Abstract: Publication date: 1 April 2017
      Source:Physica D: Nonlinear Phenomena, Volume 344
      Author(s): Asish Kumar Dhara
      We put forward a non-perturbative scheme to calculate the response of an overdamped bistable system driven by a Gaussian white noise and perturbed by a weak monochromatic force (signal) analytically. The formalism takes into account infinite number of perturbation terms of a perturbation series with amplitude of the signal as an expansion parameter. The contributions of infinite number of relaxation modes of the stochastic dynamics to the response are also taken into account in this formalism. A closed form analytic expression of the response is obtained. Only the knowledge of the first non-trivial eigenvalue and the lowest eigenfunction of the un-perturbed Fokker–Planck operator are needed to evaluate the response. The response calculated from the derived analytic expression matches fairly well with the numerical results.

      PubDate: 2017-03-01T05:09:55Z
      DOI: 10.1016/j.physd.2016.11.002
      Issue No: Vol. 344 (2017)
       
  • Elastic and inelastic collisions of swarms
    • Authors: Dieter Armbruster; Stephan Martin; Andrea Thatcher
      Pages: 45 - 57
      Abstract: Publication date: 1 April 2017
      Source:Physica D: Nonlinear Phenomena, Volume 344
      Author(s): Dieter Armbruster, Stephan Martin, Andrea Thatcher
      Scattering interactions of swarms in potentials that are generated by an attraction–repulsion model are studied. In free space, swarms in this model form a well-defined steady state describing the translation of a stable formation of the particles whose shape depends on the interaction potential. Thus, the collision between a swarm and a boundary or between two swarms can be treated as (quasi)-particle scattering. Such scattering experiments result in internal excitations of the swarm or in bound states, respectively. In addition, varying a parameter linked to the relative importance of damping and potential forces drives transitions between elastic and inelastic scattering of the particles. By tracking the swarm’s center of mass, a refraction rule is derived via simulations relating the incoming and outgoing directions of a swarm hitting the wall. Iterating the map derived from the refraction law allows us to predict and understand the dynamics and bifurcations of swarms in square boxes and in channels.

      PubDate: 2017-03-01T05:09:55Z
      DOI: 10.1016/j.physd.2016.11.008
      Issue No: Vol. 344 (2017)
       
  • Swarming in bounded domains
    • Authors: Dieter Armbruster; Sébastien Motsch; Andrea Thatcher
      Pages: 58 - 67
      Abstract: Publication date: 1 April 2017
      Source:Physica D: Nonlinear Phenomena, Volume 344
      Author(s): Dieter Armbruster, Sébastien Motsch, Andrea Thatcher
      The Vicsek model is a prototype for the emergence of collective motion. In free space, it is characterized by a swarm of particles all moving in the same direction. Since this dynamic does not include attraction among particles, the swarm, while aligning in velocity space, has no spatial coherence. Adding specular reflection at the boundaries generates global spatial coherence of the swarms while maintaining its velocity alignment. We investigate numerically how the geometry of the domain influences the Vicsek model using three type of geometry: a channel, a disk and a rectangle. Varying the parameters of the Vicsek model (e.g. noise levels and influence horizons), we discuss the mechanisms that generate spatial coherence and show how they create new dynamical solutions of the swarming motions in these geometries. Several observables are introduced to characterize the simulated patterns (e.g. mass profile, center of mass, connectivity of the swarm).

      PubDate: 2017-03-01T05:09:55Z
      DOI: 10.1016/j.physd.2016.11.009
      Issue No: Vol. 344 (2017)
       
  • Self-assembly of a filament by curvature-inducing proteins
    • Authors: James Kwiecinski; S. Jonathan Chapman; Alain Goriely
      Pages: 68 - 80
      Abstract: Publication date: 1 April 2017
      Source:Physica D: Nonlinear Phenomena, Volume 344
      Author(s): James Kwiecinski, S. Jonathan Chapman, Alain Goriely
      We explore a simplified macroscopic model of membrane shaping by means of curvature-sensing BAR proteins. Equations describing the interplay between the shape of a freely floating filament in a fluid and the adhesion kinetics of proteins are derived from mechanical principles. The constant curvature solutions that arise from this system are studied using weakly nonlinear analysis. We show that the stability of the filament’s shape is completely characterized by the parameters associated with protein recruitment and establish that in the bistable regime, proteins aggregate on the filament forming regions of high and low curvatures. This pattern formation is then followed by phase-coarsening that resolves on a time-scale dependent on protein diffusion and drift across the filament, which contend to smooth and maintain the pattern respectively. The model is generalized for multiple species of BAR proteins and we show that the stability of the assembled shape is determined by a competition between proteins attaching on opposing sides.

      PubDate: 2017-03-01T05:09:55Z
      DOI: 10.1016/j.physd.2016.12.001
      Issue No: Vol. 344 (2017)
       
  • Corrigendum to “Fluctuations induced transition of localization of
           granular objects caused by degrees of crowding” [Physica D 336 (2016)
           39-46]
    • Authors: Soutaro Oda; Yoshitsugu Kubo; Chwen-Yang Shew; Kenichi Yoshikawa
      First page: 81
      Abstract: Publication date: 1 April 2017
      Source:Physica D: Nonlinear Phenomena, Volume 344
      Author(s): Soutaro Oda, Yoshitsugu Kubo, Chwen-Yang Shew, Kenichi Yoshikawa


      PubDate: 2017-03-01T05:09:55Z
      DOI: 10.1016/j.physd.2017.02.006
      Issue No: Vol. 344 (2017)
       
  • Low-dimensional reduced-order models for statistical response and
           uncertainty quantification: Barotropic turbulence with topography
    • Authors: Di Qi; Andrew J. Majda
      Pages: 7 - 27
      Abstract: Publication date: 15 March 2017
      Source:Physica D: Nonlinear Phenomena, Volume 343
      Author(s): Di Qi, Andrew J. Majda
      A low-dimensional reduced-order statistical closure model is developed for quantifying the uncertainty to changes in forcing in a barotropic turbulent system with topography involving interactions between small-scale motions and a large-scale mean flow. Imperfect model sensitivity is improved through a recent mathematical strategy for calibrating model errors in a training phase, where information theory and linear statistical response theory are combined in a systematic fashion to achieve the optimal model parameters. Statistical theories about a Gaussian invariant measure and the exact statistical energy equations are also developed for the truncated barotropic equations that can be used to improve the imperfect model prediction skill. A stringent paradigm model of 57 degrees of freedom is used to display the feasibility of the reduced-order methods. This simple model creates large-scale zonal mean flow shifting directions from westward to eastward jets with an abrupt change in amplitude when perturbations are applied, and prototype blocked and unblocked patterns can be generated in this simple model similar to the real natural system. Principal statistical responses in mean and variance can be captured by the reduced-order models with desirable accuracy and efficiency with only 3 resolved modes. An even more challenging regime with non-Gaussian equilibrium statistics using the fluctuation equations is also tested in the reduced-order models with accurate prediction using the first 5 resolved modes. These reduced-order models also show potential for uncertainty quantification and prediction in more complex realistic geophysical turbulent dynamical systems.

      PubDate: 2017-02-09T06:01:16Z
      DOI: 10.1016/j.physd.2016.11.006
      Issue No: Vol. 343 (2017)
       
  • Isolating blocks as computational tools in the circular restricted
           three-body problem
    • Authors: Rodney L. Anderson; Robert W. Easton; Martin W. Lo
      Pages: 38 - 50
      Abstract: Publication date: 15 March 2017
      Source:Physica D: Nonlinear Phenomena, Volume 343
      Author(s): Rodney L. Anderson, Robert W. Easton, Martin W. Lo
      Isolating blocks may be used as computational tools to search for the invariant manifolds of orbits and hyperbolic invariant sets associated with libration points while also giving additional insight into the dynamics of the flow in these regions. We use isolating blocks to investigate the dynamics of objects entering the Earth–Moon system in the circular restricted three-body problem with energies close to the energy of the L 2 libration point. Specifically, the stable and unstable manifolds of Lyapunov orbits and the hyperbolic invariant set around the libration points are obtained by numerically computing the way orbits exit from an isolating block in combination with a bisection method. Invariant spheres of solutions in the spatial problem may then be located using the resulting manifolds.

      PubDate: 2017-02-09T06:01:16Z
      DOI: 10.1016/j.physd.2016.10.004
      Issue No: Vol. 343 (2017)
       
  • Finite-time thin film rupture driven by modified evaporative loss
    • Authors: Hangjie Ji; Thomas P. Witelski
      Pages: 1 - 15
      Abstract: Publication date: 1 March 2017
      Source:Physica D: Nonlinear Phenomena, Volume 342
      Author(s): Hangjie Ji, Thomas P. Witelski
      Rupture is a nonlinear instability resulting in a finite-time singularity as a film layer approaches zero thickness at a point. We study the dynamics of rupture in a generalized mathematical model of thin films of viscous fluids with modified evaporative effects. The governing lubrication model is a fourth-order nonlinear parabolic partial differential equation with a non-conservative loss term. Several different types of finite-time singularities are observed due to balances between conservative and non-conservative terms. Non-self-similar behavior and two classes of self-similar rupture solutions are analyzed and validated against high resolution PDE simulations.

      PubDate: 2017-01-14T04:47:15Z
      DOI: 10.1016/j.physd.2016.10.002
      Issue No: Vol. 342 (2017)
       
  • Stability on time-dependent domains: convective and dilution effects
    • Authors: R. Krechetnikov; E. Knobloch
      Pages: 16 - 23
      Abstract: Publication date: 1 March 2017
      Source:Physica D: Nonlinear Phenomena, Volume 342
      Author(s): R. Krechetnikov, E. Knobloch
      We explore near-critical behavior of spatially extended systems on time-dependent spatial domains with convective and dilution effects due to domain flow. As a paradigm, we use the Swift–Hohenberg equation, which is the simplest nonlinear model with a non-zero critical wavenumber, to study dynamic pattern formation on time-dependent domains. A universal amplitude equation governing weakly nonlinear evolution of patterns on time-dependent domains is derived and proves to be a generalization of the standard Ginzburg–Landau equation. Its key solutions identified here demonstrate a substantial variety–spatially periodic states with a time-dependent wavenumber, steady spatially non-periodic states, and pulse-train solutions–in contrast to extended systems on time-fixed domains. The effects of domain flow, such as bifurcation delay due to domain growth and destabilization due to oscillatory domain flow, on the Eckhaus instability responsible for phase slips in spatially periodic states are analyzed with the help of both local and global stability analyses. A nonlinear phase equation describing the approach to a phase-slip event is derived. Detailed analysis of a phase slip using multiple time scale methods demonstrates different mechanisms governing the wavelength changing process at different stages.

      PubDate: 2017-01-14T04:47:15Z
      DOI: 10.1016/j.physd.2016.10.003
      Issue No: Vol. 342 (2017)
       
  • Invariant manifolds and the parameterization method in coupled energy
           harvesting piezoelectric oscillators
    • Abstract: Publication date: Available online 19 April 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): Albert Granados
      Energy harvesting systems based on oscillators aim to capture energy from mechanical oscillations and convert it into electrical energy. Widely extended are those based on piezoelectric materials, whose dynamics are Hamiltonian submitted to different sources of dissipation: damping and coupling. These dissipations bring the system to low energy regimes, which is not desired in long term as it diminishes the absorbed energy. To avoid or to minimize such situations, we propose that the coupling of two oscillators could benefit from theory of Arnold diffusion. Such phenomenon studies O ( 1 ) energy variations in Hamiltonian systems and hence could be very useful in energy harvesting applications. This article is a first step towards this goal. We consider two piezoelectric beams submitted to a small forcing and coupled through an electric circuit. By considering the coupling, damping and forcing as perturbations, we prove that the unperturbed system possesses a 4-dimensional Normally Hyperbolic Invariant Manifold with 5 and 4-dimensional stable and unstable manifolds, respectively. These are locally unique after the perturbation. By means of the parameterization method, we numerically compute parameterizations of the perturbed manifold, its stable and unstable manifolds and study its inner dynamics. We show evidence of homoclinic connections when the perturbation is switched on.

      PubDate: 2017-04-25T10:34:15Z
       
  • The spectrum of the torus profile to a geometric variational problem with
           long range interaction
    • Abstract: Publication date: Available online 18 April 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): Xiaofeng Ren, Juncheng Wei
      The profile problem for the Ohta-Kawasaki diblock copolymer theory is a geometric variational problem. The energy functional is defined on sets in R 3 of prescribed volume and the energy of an admissible set is its perimeter plus a long range interaction term related to the Newtonian potential of the set. This problem admits a solution, called a torus profile, that is a set enclosed by an approximate torus of the major radius 1 and the minor radius q . The torus profile is both axially symmetric about the z axis and reflexively symmetric about the x y -plane. There is a way to set up the profile problem in a function space as a partial differential-integro equation. The linearized operator L of the problem at the torus profile is decomposed into a family of linear ordinary differential-integro operators L m where the index m = 0 , 1 , 2 , . . . is called a mode. The spectrum of L is the union of the spectra of the L m ’s. It is proved that for each m , when q is sufficiently small, L m is positive definite. ( 0 is an eigenvalue for both L 0 and L 1 , due to the translation and rotation invariance.) As q tends to 0 , more and more L m ’s become positive definite. However no matter how small q is, there is always a mode m of which L m has a negative eigenvalue. This mode grows to infinity like q − 3 / 4 as q → 0 .

      PubDate: 2017-04-25T10:34:15Z
       
  • Dynamical and energetic instabilities of F=2 spinor Bose-Einstein
           condensates in an optical lattice
    • Authors: Deng-Shan Wang; Yu-Ren Shi; Wen-Xing Feng; Lin Wen
      Abstract: Publication date: Available online 17 April 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): Deng-Shan Wang, Yu-Ren Shi, Wen-Xing Feng, Lin Wen
      The dynamical and energetic instabilities of the F =2 spinor Bose-Einstein condensates in an optical lattice are investigated theoretically and numerically. By analyzing the dynamical response of different carrier waves to an additional linear perturbation, we obtain the instability criteria for the ferromagnetic, uniaxial nematic, biaxial nematic and cyclic states, respectively. When an external magnetic field is taken into account, we find that the linear or quadratic Zeeman effects obviously affect the dynamical instability properties of uniaxial nematic, biaxial nematic and cyclic states, but not for the ferromagnetic one. In particular, it is found that the faster moving F =2 spinor BEC has a larger energetic instability region than lower one in all the four states. In addition, it is seen that for most states there probably exists a critical value k c > 0 , for which k > k c gives the energetic instability to arise under appreciative parameters.

      PubDate: 2017-04-18T03:43:03Z
      DOI: 10.1016/j.physd.2017.04.002
       
  • On the phenomenon of mixed dynamics in Pikovsky-Topaj system of coupled
           rotators
    • Authors: A.S. Gonchenko; S.V. Gonchenko; A.O. Kazakov; D.V. Turaev
      Abstract: Publication date: Available online 30 March 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): A.S. Gonchenko, S.V. Gonchenko, A.O. Kazakov, D.V. Turaev
      A one-parameter family of time-reversible systems on three-dimensional torus is considered. It is shown that the dynamics is not conservative, namely the attractor and repeller intersect but not coincide. We explain this as the manifestation of the so-called mixed dynamics phenomenon which corresponds to a persistent intersection of the closure of the stable periodic orbits and the closure of the completely unstable periodic orbits. We search for the stable and unstable periodic orbits indirectly, by finding non-conservative saddle periodic orbits and heteroclinic connections between them. In this way, we are able to claim the existence of mixed dynamics for a large range of parameter values. We investigate local and global bifurcations that can be used for the detection of mixed dynamics.

      PubDate: 2017-04-04T03:13:49Z
      DOI: 10.1016/j.physd.2017.02.002
       
  • Pattern formation on the free surface of a ferrofluid: Spatial dynamics
           and homoclinic bifurcation
    • Authors: M.D. Groves; D.J.B. Lloyd; A. Stylianou
      Abstract: Publication date: Available online 23 March 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): M.D. Groves, D.J.B. Lloyd, A. Stylianou
      We establish the existence of spatially localised one-dimensional free surfaces of a ferrofluid near onset of the Rosensweig instability, assuming a general (nonlinear) magnetisation law. It is shown that the ferrohydrostatic equations can be derived from a variational principle that allows one to formulate them as an (infinite-dimensional) spatial Hamiltonian system in which the unbounded free-surface direction plays the role of time. A centre-manifold reduction technique converts the problem for small solutions near onset to an equivalent Hamiltonian system with finitely many degrees of freedom. Normal-form theory yields the existence of homoclinic solutions to the reduced system, which correspond to spatially localised solutions of the ferrohydrostatic equations.

      PubDate: 2017-03-28T02:42:26Z
      DOI: 10.1016/j.physd.2017.03.004
       
  • Synchronization of weakly coupled canard oscillators
    • Authors: Elif Köksal Ersöz; Mathieu Desroches; Martin Krupa
      Abstract: Publication date: Available online 22 March 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): Elif Köksal Ersöz, Mathieu Desroches, Martin Krupa
      Synchronization has been studied extensively in the context of weakly coupled oscillators using the so-called phase response curve (PRC) which measures how a change of the phase of an oscillator is affected by a small perturbation. This approach was based upon the work of Malkin, and it has been extended to relaxation oscillators. Namely, synchronization conditions were established under the weak coupling assumption, leading to a criterion for the existence of synchronous solutions of weakly coupled relaxation oscillators. Previous analysis relies on the fact that the slow nullcline does not intersect the fast nullcline near one of its fold points, where canard solutions can arise. In the present study we use numerical continuation techniques to solve the adjoint equations and we show that synchronization properties of canard cycles are different than those of classical relaxation cycles. In particular, we highlight a new special role of the maximal canard in separating two distinct synchronization regimes: the Hopf regime and the relaxation regime. Phase plane analysis of slow-fast oscillators undergoing a canard explosion provides an explanation for this change of synchronization properties across the maximal canard.

      PubDate: 2017-03-28T02:42:26Z
      DOI: 10.1016/j.physd.2017.02.016
       
  • Integrable systems and invariant curve flows in symplectic Grassmannian
           space
    • Authors: Junfeng Song; Changzheng Qu; Ruoxia Yao
      Abstract: Publication date: Available online 21 March 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): Junfeng Song, Changzheng Qu, Ruoxia Yao
      In this paper, local geometry of curves in the symplectic Grassmannian homogeneous space Sp ( 4 , R ) / ( Sp ( 2 , R ) × Sp ( 2 , R ) ) and its connection with that of the pseudo-hyperbolic space H 2 , 2 are studied. The group-based Serret-Frenet equations and the associated Maurer-Cartan differential invariants for the Grassmannian curves are obtained by using the equivariant moving frame method. The Grassmannian natural frame are also constructed by a gauge transformation from the Serret-Frenet frame, relating to the hyperbolic natural frame by the local Lie group isomorphism. Using the natural frames, invariant curve flows in the Grassmannian and the hyperbolic spaces are studied. It is shown that certain intrinsic curve flows induce the bi-Hamiltonian integrable matrix mKdV equation on the Maurer-Cartan differential invariants.

      PubDate: 2017-03-28T02:42:26Z
      DOI: 10.1016/j.physd.2017.02.013
       
  • Global existence of solutions to a tear film model with locally elevated
           evaporation rates
    • Authors: Yuan Gao; Hangjie Ji; Jian-Guo Liu; Thomas P. Witelski
      Abstract: Publication date: Available online 21 March 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): Yuan Gao, Hangjie Ji, Jian-Guo Liu, Thomas P. Witelski
      Motivated by a model proposed by Peng et al. [Advances in Coll. and Interf. Sci. 206 (2014)] for break-up of tear films on human eyes, we study the dynamics of a generalized thin film model. The governing equations form a fourth-order coupled system of nonlinear parabolic PDEs for the film thickness and salt concentration subject to non-conservative effects representing evaporation. We analytically prove the global existence of solutions to this model with mobility exponents in several different ranges and present numerical simulations that are in agreement with the analytic results. We also numerically capture other interesting dynamics of the model, including finite-time rupture-shock phenomenon due to the instabilities caused by locally elevated evaporation rates, convergence to equilibrium and infinite-time thinning.

      PubDate: 2017-03-28T02:42:26Z
      DOI: 10.1016/j.physd.2017.03.005
       
  • Stability of the phase motion in race-track microtons
    • Authors: Yu.A. Kubyshin; O. Larreal; R. Ramírez-Ros; T.M. Seara
      Abstract: Publication date: Available online 18 March 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): Yu.A. Kubyshin, O. Larreal, R. Ramírez-Ros, T.M. Seara
      We model the phase oscillations of electrons in race-track microtrons by means of an area preserving map with a fixed point at the origin, which represents the synchronous trajectory of a reference particle in the beam. We study the nonlinear stability of the origin in terms of the synchronous phase —the phase of the synchronous particle at the injection. We estimate the size and shape of the stability domain around the origin, whose main connected component is enclosed by an invariant curve. We describe the evolution of the stability domain as the synchronous phase varies. We also clarify the role of the stable and unstable invariant curves of some hyperbolic (fixed or periodic) points.

      PubDate: 2017-03-20T19:31:07Z
      DOI: 10.1016/j.physd.2017.03.001
       
  • Markovian properties of velocity increments in boundary layer turbulence
    • Authors: Murat Tutkun
      Abstract: Publication date: Available online 16 March 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): Murat Tutkun
      Markovian properties of the turbulent velocity increments in a flat plate boundary layer at Re θ = 19100 are investigated using hot-wire anemometry measurements of the streamwise velocity component in a wind tunnel. Increments of the longitudinal velocities at different wall-normal positions show that the flow exhibits Markovian properties when the separation between different scales, or the Markov-Einstein coherence length, is on the order of the Taylor microscale, λ . The results indicate that Markovian nature of turbulence evolves across the boundary layer showing certain characteristics pertaining to the distance to the wall. The connection between the Markovian properties of turbulent boundary layer and existence of the spectral gap is explored. Markovianity of the process is also discussed in relation to the nonlocal nonlinear versus local nonlinear transfer of energy, triadic interactions and dissipation.

      PubDate: 2017-03-20T19:31:07Z
      DOI: 10.1016/j.physd.2017.03.002
       
  • Targeted energy transfer in laminar vortex-induced vibration of a sprung
           cylinder with a nonlinear dissipative rotator
    • Authors: Antoine Blanchard; Lawrence A. Bergman; Alexander F. Vakakis
      Abstract: Publication date: Available online 16 March 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): Antoine Blanchard, Lawrence A. Bergman, Alexander F. Vakakis
      We computationally investigate the dynamics of a linearly-sprung circular cylinder immersed in an incompressible flow and undergoing transverse vortex-induced vibration (VIV), to which is attached a rotational nonlinear energy sink (NES) consisting of a mass that freely rotates at constant radius about the cylinder axis, and whose motion is restrained by a rotational linear viscous damper. The inertial coupling between the rotational motion of the attached mass and the rectilinear motion of the cylinder is “essentially nonlinear”, which, in conjunction with dissipation, allows for one-way, nearly irreversible targeted energy transfer (TET) from the oscillating cylinder to the nonlinear dissipative attachment. At the intermediate Reynolds number R e = 100 , the NES-equipped sprung cylinder undergoes repetitive cycles of slowly decaying oscillations punctuated by intervals of chaotic instabilities. During the slowly decaying portion of each cycle, the dynamics of the cylinder is regular and, for large enough values of the ratio ε of the NES mass to the total mass (i.e., NES mass plus cylinder mass), can lead to significant vortex street elongation with partial stabilization of the wake. As ε approaches zero, no such vortex elongation is observed and the wake patterns appear similar to that for a sprung cylinder with no NES. We apply proper orthogonal decomposition (POD) to the velocity flow field during a slowly decaying portion of the solution and show that, in situations where vortex elongation occurs, the NES, though not in direct contact with the surrounding fluid, has a drastic effect on the underlying flow structures, imparting significant and continuous passive redistribution of energy among POD modes. We construct a POD-based reduced-order model for the lift coefficient to characterize energy transactions between the fluid and the cylinder throughout the slowly decaying cycle. We introduce a quantitative signed measure of the work done by the fluid on the cylinder over one quasi-period of the slowly decaying response and find that vortex elongation is associated with a sign change of that measure, indicating that a reversal of the direction of energy transfer, with the cylinder “leaking energy back” to the flow, is responsible for partial stabilization and elongation of the wake. We interpret these findings in terms of the spatial structure and energy distribution of the POD modes, and relate them to the mechanism of transient resonance capture into a slow invariant manifold of the fluid–structure interaction dynamics.

      PubDate: 2017-03-20T19:31:07Z
      DOI: 10.1016/j.physd.2017.03.003
       
  • Fluctuations, response, and resonances in a simple atmospheric model
    • Authors: Andrey Gritsun; Valerio Lucarini
      Abstract: Publication date: Available online 14 March 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): Andrey Gritsun, Valerio Lucarini
      We study the response of a simple quasi-geostrophic barotropic model of the atmosphere to various classes of perturbations affecting its forcing and its dissipation using the formalism of the Ruelle response theory. We investigate the geometry of such perturbations by constructing the covariant Lyapunov vectors of the unperturbed system and discover in one specific case–orographic forcing–a substantial projection of the forcing onto the stable directions of the flow. This results into a resonant response shaped as a Rossby-like wave that has no resemblance to the unforced variability in the same range of spatial and temporal scales. Such a climatic surprise corresponds to a violation of the fluctuation-dissipation theorem, in agreement with the basic tenets of nonequilibrium statistical mechanics. The resonance can be attributed to a specific group of rarely visited unstable periodic orbits of the unperturbed system. Our results reinforce the idea of using basic methods of nonequilibrium statistical mechanics and high-dimensional chaotic dynamical systems to approach the problem of understanding climate dynamics.

      PubDate: 2017-03-20T19:31:07Z
      DOI: 10.1016/j.physd.2017.02.015
       
  • Standing and travelling waves in a spherical brain model: The Nunez model
           revisited
    • Authors: S. Visser; R. Nicks; O. Faugeras; S. Coombes
      Abstract: Publication date: Available online 8 March 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): S. Visser, R. Nicks, O. Faugeras, S. Coombes
      The Nunez model for the generation of electroencephalogram (EEG) signals is naturally described as a neural field model on a sphere with space-dependent delays. For simplicity, dynamical realisations of this model either as a damped wave equation or an integro-differential equation, have typically been studied in idealised one dimensional or planar settings. Here we revisit the original Nunez model to specifically address the role of spherical topology on spatio-temporal pattern generation. We do this using a mixture of Turing instability analysis, symmetric bifurcation theory, center manifold reduction and direct simulations with a bespoke numerical scheme. In particular we examine standing and travelling wave solutions using normal form computation of primary and secondary bifurcations from a steady state. Interestingly, we observe spatio-temporal patterns which have counterparts seen in the EEG patterns of both epileptic and schizophrenic brain conditions.

      PubDate: 2017-03-12T21:31:41Z
      DOI: 10.1016/j.physd.2017.02.017
       
  • Controlling coexisting attractors of an impacting system via linear
           augmentation
    • Authors: Yang Liu; Joseph Páez Chávez
      Abstract: Publication date: Available online 8 March 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): Yang Liu, Joseph Páez Chávez
      This paper studies the control of coexisting attractors in an impacting system via a recently developed control law based on linear augmentation. Special attention is given to two control issues in the framework of multistable engineering systems, namely, the switching between coexisting attractors without altering the system’s main parameters and the avoidance of grazing-induced chaotic responses. The effectiveness of the proposed control scheme is confirmed numerically for the case of a periodically excited, soft impact oscillator. Our analysis shows how path-following techniques for non-smooth systems can be used in order to determine the optimal control parameters in terms of energy expenditure due to the control signal and transient behavior of the control error, which can be applied to a broad range of engineering problems.

      PubDate: 2017-03-12T21:31:41Z
      DOI: 10.1016/j.physd.2017.02.018
       
  • Construction of Darboux coordinates and Poincaré-Birkhoff normal forms in
           noncanonical Hamiltonian systems
    • Authors: Andrej Junginger; Jörg Main; Günter Wunner
      Abstract: Publication date: Available online 7 March 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): Andrej Junginger, Jörg Main, Günter Wunner
      We demonstrate a general method to construct Darboux coordinates via normal form expansions in noncanonical Hamiltonian system obtained from e.g. a variational approach to quantum systems. The procedure serves as a tool to naturally extract canonical coordinates out of the variational parameters and at the same time to transform the energy functional into its Poincaré-Birkhoff normal form. The method is general in the sense that it is applicable for arbitrary degrees of freedom, in arbitrary orders of the local expansion, and it is independent of the precise form of the Hamilton operator. The method presented allows for the general and systematic investigation of quantum systems in the vicinity of fixed points, which e.g. correspond to ground, excited or transition states. Moreover, it directly allows to calculate classical and quantum reaction rates by applying transition state theory.

      PubDate: 2017-03-12T21:31:41Z
      DOI: 10.1016/j.physd.2017.02.014
       
  • Assessment of the effects of azimuthal mode number perturbations upon the
           implosion processes of fluids in cylinders
    • Authors: Michael Lindstrom
      Abstract: Publication date: Available online 1 March 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): Michael Lindstrom
      Fluid instabilities arise in a variety of contexts and are often unwanted results of engineering imperfections. In one particular model for a magnetized target fusion reactor, a pressure wave is propagated in a cylindrical annulus comprised of a dense fluid before impinging upon a plasma and imploding it. Part of the success of the apparatus is a function of how axially-symmetric the final pressure pulse is upon impacting the plasma. We study a simple model for the implosion of the system to study how imperfections in the pressure imparted on the outer circumference grow due to geometric focusing. Our methodology entails linearizing the compressible Euler equations for mass and momentum conservation about a cylindrically symmetric problem and analyzing the perturbed profiles at different mode numbers. The linearized system gives rise to singular shocks and through analyzing the perturbation profiles at various times, we infer that high mode numbers are dampened through the propagation. We also study the Linear Klein-Gordon equation in the context of stability of linear cylindrical wave formation whereby highly oscillatory, bounded behaviour is observed in a far field solution.

      PubDate: 2017-03-07T21:14:06Z
      DOI: 10.1016/j.physd.2017.02.012
       
  • KdV cnoidal waves in a traffic flow model with periodic boundaries
    • Authors: L.L. Hattam
      Abstract: Publication date: Available online 1 March 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): L.L. Hattam
      An optimal-velocity (OV) model describes car motion on a single lane road. In particular, near to the boundary signifying the onset of traffic jams, this model reduces to a perturbed Korteweg-de Vries (KdV) equation using asymptotic analysis. Previously, the KdV soliton solution has then been found and compared to numerical results (see Muramatsu and Nagatani (1999)). Here, we instead apply modulation theory to this perturbed KdV equation to obtain at leading order, the modulated cnoidal wave solution. At the next order, the Whitham equations are derived, which have been modified due to the equation perturbation terms. Next, from this modulation system, a family of spatially periodic cnoidal waves are identified that characterise vehicle headway distance. Then, for this set of solutions, we establish the relationship between the wave speed, the modulation term and the driver sensitivity. This analysis is confirmed with comparisons to numerical solutions of the OV model. As well, the long-time behaviour of these solutions is investigated.

      PubDate: 2017-03-07T21:14:06Z
      DOI: 10.1016/j.physd.2017.02.010
       
  • Controlling roughening processes in the stochastic Kuramoto-Sivashinsky
           equation
    • Authors: S.N. Gomes; S. Kalliadasis; D.T. Papageorgiou; G.A. Pavliotis; M. Pradas
      Abstract: Publication date: Available online 1 March 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): S.N. Gomes, S. Kalliadasis, D.T. Papageorgiou, G.A. Pavliotis, M. Pradas
      We present a novel control methodology to control the roughening processes of semilinear parabolic stochastic partial differential equations in one dimension, which we exemplify with the stochastic Kuramoto-Sivashinsky equation. The original equation is split into a linear stochastic and a nonlinear deterministic equation so that we can apply linear feedback control methods. Our control strategy is then based on two steps: first, stabilize the zero solution of the deterministic part and, second, control the roughness of the stochastic linear equation. We consider both periodic controls and point actuated ones, observing in all cases that the second moment of the solution evolves in time according to a power-law until it saturates at the desired controlled value.

      PubDate: 2017-03-07T21:14:06Z
      DOI: 10.1016/j.physd.2017.02.011
       
  • A novel route to a Hopf bifurcation scenario in switched systems with
           dead-zone
    • Authors: P. Kowalczyk
      Abstract: Publication date: Available online 1 March 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): P. Kowalczyk
      Planar switched systems with dead-zone are analyzed. In particular, we consider the effects of a perturbation which is applied to a linear control law and, due to the perturbation, the control changes from purely positional to position-velocity control. This type of a perturbation leads to a novel Hopf-like discontinuity induced bifurcation. We show that this bifurcation leads to the creation of a small scale limit cycle attractor, which scales as the square root of the bifurcation parameter. We then investigate numerically a planar switched system with a positional feedback law, dead-zone and time delay in the switching function. Using the same parameter values as for the switched system without time delay in the switching function, we show a Hopf-like bifurcation scenario which exhibits a qualitative and a quantitative agreement with the scenario analyzed for the non-delayed system.

      PubDate: 2017-03-07T21:14:06Z
      DOI: 10.1016/j.physd.2017.02.007
       
  • Hopf and Homoclinic Bifurcations on the sliding vector field of switching
           systems in R3: A case study in power electronics
    • Authors: Rony Cristiano; Tiago Carvalho; Durval J. Tonon; Daniel J. Pagano
      Abstract: Publication date: Available online 24 February 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): Rony Cristiano, Tiago Carvalho, Durval J. Tonon, Daniel J. Pagano
      In this paper, Hopf and homoclinic bifurcations that occur in the sliding vector field of switching systems in R 3 are studied. In particular, a dc-dc boost converter with sliding mode control and washout filter is analyzed. This device is modelled as a three-dimensional Filippov system, characterized by the existence of sliding movement and restricted to the switching manifold. The operating point of the converter is a stable pseudo-equilibrium and it undergoes a subcritical Hopf bifurcation. Such a bifurcation occurs in the sliding vector field and creates, in this field, an unstable limit cycle. The limit cycle is connected to the switching manifold and disappears when it touches the visible-invisible two-fold point, resulting in an homoclinic loop which itself closes in this two-fold point. The study of these dynamic phenomena that can be found in different power electronic circuits controlled by sliding mode control strategies are relevant from the viewpoint of the global stability and robustness of the control design.

      PubDate: 2017-03-01T05:09:55Z
      DOI: 10.1016/j.physd.2017.02.005
       
  • Axisymmetric pulse train solutions in narrow-gap spherical Couette flow
    • Authors: Adam Child; Rainer Hollerbach; Evy Kersalé
      Abstract: Publication date: Available online 24 February 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): Adam Child, Rainer Hollerbach, Evy Kersalé
      We numerically compute the flow induced in a spherical shell by fixing the outer sphere and rotating the inner one. The aspect ratio ϵ = ( r o − r i ) / r i is set at 0.04 and 0.02, and in each case the Reynolds number measuring the inner sphere’s rotation rate is increased to ∼ 10% beyond the first bifurcation from the basic state flow. For ϵ = 0.04 the initial bifurcations are the same as in previous numerical work at ϵ = 0.154 , and result in steady one- and two-vortex states. Further bifurcations yield travelling wave solutions similar to previous analytic results valid in the ϵ → 0 limit. For ϵ = 0.02 the steady one-vortex state no longer exists, and the first bifurcation is directly to these travelling wave solutions, consisting of pulse trains of Taylor vortices travelling toward the equator from both hemispheres, and annihilating there in distinct phase-slip events. We explore these time-dependent solutions in detail, and find that they can be both equatorially symmetric and asymmetric, as well as periodic or quasi-periodic in time.

      PubDate: 2017-03-01T05:09:55Z
      DOI: 10.1016/j.physd.2017.02.009
       
  • Assimilating Eulerian and Lagrangian data in traffic-flow models
    • Authors: Chao Xia; Courtney Cochrane; Joseph DeGuire; Gaoyang Fan; Emma Holmes; Melissa McGuirl; Patrick Murphy; Jenna Palmer; Paul Carter; Laura Slivinski; Björn Sandstede
      Abstract: Publication date: Available online 21 February 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): Chao Xia, Courtney Cochrane, Joseph DeGuire, Gaoyang Fan, Emma Holmes, Melissa McGuirl, Patrick Murphy, Jenna Palmer, Paul Carter, Laura Slivinski, Björn Sandstede
      Data assimilation of traffic flow remains a challenging problem. One difficulty is that data come from different sources ranging from stationary sensors and camera data to GPS and cell phone data from moving cars. Sensors and cameras give information about traffic density, while GPS data provide information about the positions and velocities of individual cars. Previous methods for assimilating Lagrangian data collected from individual cars relied on specific properties of the underlying computational model or its reformulation in Lagrangian coordinates. These approaches make it hard to assimilate both Eulerian density and Lagrangian positional data simultaneously. In this paper, we propose an alternative approach that allows us to assimilate both Eulerian and Lagrangian data. We show that the proposed algorithm is accurate and works well in different traffic scenarios and regardless of whether ensemble Kalman or particle filters are used. We also show that the algorithm is capable of estimating parameters and assimilating real traffic observations and synthetic observations obtained from microscopic models.

      PubDate: 2017-02-21T09:49:54Z
      DOI: 10.1016/j.physd.2017.02.004
       
  • Complex predator invasion waves in a Holling-Tanner model with nonlocal
           prey interaction
    • Authors: A. Bayliss; V.A. Volpert
      Abstract: Publication date: Available online 20 February 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): A. Bayliss, V.A. Volpert
      We consider predator invasions for the nonlocal Holling-Tanner model. Predators are introduced in a small region adjacent to an extensive predator-free region. In its simplest form an invasion front propagates into the predator-free region with a predator-prey coexistence state displacing the predator-free state. However, patterns may form in the wake of the invasion front due to instability of the coexistence state. The coexistence state can be subject to either oscillatory or cellular instability, depending on parameters. Furthermore, the oscillatory instability can be either at zero wave number or finite wave number. In addition, the (unstable) predator-free state can be subject to additional cellular instabilities when the extent of the nonlocality is sufficiently large. We perform numerical simulations that demonstrate that the invasion wave may have a complex structure in which different spatial regions exhibit qualitatively different behaviors. These regions are separated by relatively narrow transition regions that we refer to as fronts. We also derive analytic approximations for the speeds of the fronts and find qualitative and quantitative agreement with the results of computations.

      PubDate: 2017-02-21T09:49:54Z
      DOI: 10.1016/j.physd.2017.02.003
       
  • Elementary solutions for a model Boltzmann equation in one dimension and
           the connection to grossly determined solutions
    • Authors: Thomas E. Carty
      Abstract: Publication date: Available online 20 February 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): Thomas E. Carty
      The Fourier-transformed version of the time dependent slip-flow model Boltzmann equation associated with the linearized BGK model is solved in order to determine the solution’s asymptotics. The ultimate goal of this paper is to demonstrate that there exists a robust set of solutions to this model Boltzmann equation that possess a special property that was conjectured by Truesdell and Muncaster: that solutions decay to a subclass of the solution set uniquely determined by the initial mass density of the gas called the grossly determined solutions. First we determine the spectrum and eigendistributions of the associated homogeneous equation. Then, using Case’s method of elementary solutions, we find analytic time-dependent solutions to the model Boltzmann equation for initial data with a specialized compact support condition under the Fourier transform. In doing so, we show that the spectrum separates the solutions into two distinct parts: one that behaves as a set of transient solutions and the other limiting to a stable subclass of solutions. Thus, we demonstrate that for gas flows with this specialized initial density condition, in time all gas flows for the one dimensional model Boltzmann equation act as grossly determined solutions.

      PubDate: 2017-02-21T09:49:54Z
      DOI: 10.1016/j.physd.2017.02.008
       
  • Bright and dark solitons in the unidirectional long wave limit for the
           energy transfer on anharmonic crystal lattices
    • Authors: Luis A. Cisneros-Ake; José F. Solano Peláez
      Abstract: Publication date: Available online 9 February 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): Luis A. Cisneros-Ake, José F. Solano Peláez
      The problem of energy transportation along a cubic anharmonic crystal lattice, in the unidirectional long wave limit, is considered. A detailed process, in the discrete lattice equations, shows that unidirectional stable propagating waves for the continuum limit produces a coupled system between a nonlinear Schrödinger (NLS) equation and the Korteweg-deVries (KdV) equation. The traveling wave formalism provides a diversity of exact solutions ranging from the classical Davydov’s soliton (subsonic and supersonic) of the first and second kind to a class consisting in the coupling between the KdV soliton and dark solitons containing the typical ones (similar to the dark-gray soliton in the standard defocusing NLS) and a new kind in the form of a two-hump dark soliton. This family of exact solutions are numerically tested, by means of the pseudo spectral method, in our NLS-KdV system.

      PubDate: 2017-02-15T09:34:42Z
      DOI: 10.1016/j.physd.2017.02.001
       
  • The Lyapunov-Krasovskii theorem and a sufficient criterion for local
           stability of isochronal synchronization in networks of delay-coupled
           oscillators
    • Authors: J.M.V. Grzybowski; E.E.N. Macau; T. Yoneyama
      Abstract: Publication date: Available online 9 February 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): J.M.V. Grzybowski, E.E.N. Macau, T. Yoneyama
      This paper presents a self-contained framework for the stability assessment of isochronal synchronization in networks of chaotic and limit-cycle oscillators. The results were based on the Lyapunov-Krasovskii theorem and they establish a sufficient condition for local synchronization stability of as a function of the system and network parameters. With this in mind, a network of mutually delay-coupled oscillators subject to direct self-coupling is considered and then the resulting error equations are block-diagonalized for the purpose of studying their stability. These error equations are evaluated by means of analytical stability results derived from the Lyapunov-Krasovskii theorem. The proposed approach is shown to be a feasible option for the investigation of local stability of isochronal synchronization for a variety of oscillators coupled through linear functions of the state variables under a given undirected graph structure. This ultimately permits the systematic identification of stability regions within the high-dimensionality of the network parameter space. Examples of applications of the results to a number of networks of delay-coupled chaotic and limit-cycle oscillators are provided, such as Lorenz, Rössler, Cubic Chua’s circuit, Van der Pol oscillator and the Hindmarsh-Rose neuron.

      PubDate: 2017-02-15T09:34:42Z
      DOI: 10.1016/j.physd.2017.01.005
       
  • Wave fronts and cascades of soliton interactions in the periodic two
           dimensional Volterra system
    • Authors: Rhys Bury; Alexander V. Mikhailov; Jing Ping Wang
      Abstract: Publication date: Available online 6 February 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): Rhys Bury, Alexander V. Mikhailov, Jing Ping Wang
      In the paper we develop the dressing method for the solution of the two-dimensional periodic Volterra system with a period N . We derive soliton solutions of arbitrary rank k and give a full classification of rank 1 solutions. We have found a new class of exact solutions corresponding to wave fronts which represent smooth interfaces between two nonlinear periodic waves or a periodic wave and a trivial (zero) solution. The wave fronts are non-stationary and they propagate with a constant average velocity. The system also has soliton solutions similar to breathers, which resembles soliton webs in the KP theory. We associate the classification of soliton solutions with the Schubert decomposition of the Grassmannians Gr R ( k , N ) and Gr C ( k , N ) .

      PubDate: 2017-02-09T06:01:16Z
      DOI: 10.1016/j.physd.2017.01.003
       
  • The stability spectrum for elliptic solutions to the focusing NLS equation
    • Authors: Bernard Deconinck; Benjamin L. Segal
      Abstract: Publication date: Available online 23 January 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): Bernard Deconinck, Benjamin L. Segal
      We present an analysis of the stability spectrum of all stationary elliptic-type solutions to the focusing Nonlinear Schrödinger equation (NLS). An analytical expression for the spectrum is given. From this expression, various quantitative and qualitative results about the spectrum are derived. Specifically, the solution parameter space is shown to be split into four regions of distinct qualitative behavior of the spectrum. Additional results on the stability of solutions with respect to perturbations of an integer multiple of the period are given, as well as a procedure for approximating the greatest real part of the spectrum.

      PubDate: 2017-01-28T05:15:28Z
      DOI: 10.1016/j.physd.2017.01.004
       
  • Reduced-space Gaussian Process Regression for data-driven probabilistic
           forecast of chaotic dynamical systems
    • Authors: Zhong Yi Wan; Themistoklis P. Sapsis
      Abstract: Publication date: Available online 5 January 2017
      Source:Physica D: Nonlinear Phenomena
      Author(s): Zhong Yi Wan, Themistoklis P. Sapsis
      We formulate a reduced-order strategy for efficiently forecasting complex high-dimensional dynamical systems entirely based on data streams. The first step of our method involves reconstructing the dynamics in a reduced-order subspace of choice using Gaussian Process Regression (GPR). GPR simultaneously allows for reconstruction of the vector field and more importantly, estimation of local uncertainty. The latter is due to (i) local interpolation error and (ii) truncation of the high-dimensional phase space. This uncertainty component can be analytically quantified in terms of the GPR hyperparameters. In the second step we formulate stochastic models that explicitly take into account the reconstructed dynamics and their uncertainty. For regions of the attractor which are not sufficiently sampled for our GPR framework to be effective, an adaptive blended scheme is formulated to enforce correct statistical steady state properties, matching those of the real data. We examine the effectiveness of the proposed method to complex systems including the Lorenz 96, the Kuramoto-Sivashinsky, as well as a prototype climate model. We also study the performance of the proposed approach as the intrinsic dimensionality of the system attractor increases in highly turbulent regimes.

      PubDate: 2017-01-14T04:47:15Z
      DOI: 10.1016/j.physd.2016.12.005
       
  • Characterizing complex networks through statistics of Möbius
           transformations
    • Authors: Vladimir Jaćimović; Aladin Crnkić
      Abstract: Publication date: Available online 31 December 2016
      Source:Physica D: Nonlinear Phenomena
      Author(s): Vladimir Jaćimović, Aladin Crnkić
      It is well-known now that dynamics of large populations of globally (all-to-all) coupled oscillators can be reduced to low-dimensional submanifolds (WS transformation and OA ansatz). Marvel et al. (2009) described an intriguing algebraic structure standing behind this reduction: oscillators evolve by the action of the group of Möbius transformations. Of course, dynamics in complex networks of coupled oscillators is highly complex and not reducible. Still, closer look unveils that even in complex networks some (possibly overlapping) groups of oscillators evolve by Möbius transformations. In this paper we study properties of the network by identifying Möbius transformations in the dynamics of oscillators. This enables us to introduce some new (statistical) concepts that characterize the network. In particular, the notion of coherence of the network (or subnetwork) is proposed. This conceptual approach is meaningful for the broad class of networks, including those with time-delayed, noisy or mixed interactions. In this paper several simple (random) graphs are studied illustrating the meaning of the concepts introduced in the paper.

      PubDate: 2017-01-05T04:02:55Z
      DOI: 10.1016/j.physd.2016.12.007
       
  • Classical quasi-steady state reduction—A mathematical
           characterization
    • Authors: Alexandra Goeke; Sebastian Walcher; Eva Zerz
      Abstract: Publication date: Available online 30 December 2016
      Source:Physica D: Nonlinear Phenomena
      Author(s): Alexandra Goeke, Sebastian Walcher, Eva Zerz
      We discuss parameter dependent polynomial ordinary differential equations that model chemical reaction networks. By classical quasi-steady state (QSS) reduction we understand the following familiar (heuristically motivated) mathematical procedure: Set the rate of change for certain (a priori chosen) variables equal to zero and use the resulting algebraic equations to obtain a system of smaller dimension for the remaining variables. This procedure will generally be valid only for certain parameter ranges. We start by showing that the reduction is accurate if and only if the corresponding parameter is what we call a QSS parameter value, and that the reduction is approximately accurate if and only if the corresponding parameter is close to a QSS parameter value. The QSS parameter values can be characterized by polynomial equations and inequations, hence parameter ranges for which QSS reduction is valid are accessible in an algorithmic manner. A defining characteristic of a QSS parameter value is that the algebraic variety defined by the QSS relations is invariant for the differential equation. A closer investigation of the associated systems shows the existence of further invariant sets; here singular perturbations enter the picture in a natural manner. We compare QSS reduction and singular perturbation reduction, and show that, while they do not agree in general, they do, up to lowest order in a small parameter, for a quite large and relevant class of examples. This observation, in turn, allows the computation of QSS reductions even in cases where an explicit resolution of the polynomial equations is not possible.

      PubDate: 2017-01-05T04:02:55Z
      DOI: 10.1016/j.physd.2016.12.002
       
  • Cascades of alternating pitchfork and flip bifurcations in H-bridge
           inverters
    • Authors: Viktor Avrutin; Zhanybai T. Zhusubaliyev; Erik Mosekilde
      Abstract: Publication date: Available online 28 December 2016
      Source:Physica D: Nonlinear Phenomena
      Author(s): Viktor Avrutin, Zhanybai T. Zhusubaliyev, Erik Mosekilde
      Power electronic DC/AC converters (inverters) play an important role in modern power engineering. These systems are also of considerable theoretical interest because their dynamics is influenced by the presence of two vastly different forcing frequencies. As a consequence, inverter systems may be modeled in terms of piecewise smooth maps with an extremely high number of switching manifolds. We have recently shown that models of this type can demonstrate a complicated bifurcation structure associated with the occurrence of border collisions. Considering the example of a PWM H-bridge single-phase inverter, the present paper discusses a number of unusual phenomena that can occur in piecewise smooth maps with a very large number of switching manifolds. We show in particular how smooth (pitchfork and flip) bifurcations may form a macroscopic pattern that stretches across the overall bifurcation structure. We explain the observed bifurcation phenomena, show under which conditions they occur, and describe them quantitatively by means of an analytic approximation.

      PubDate: 2017-01-05T04:02:55Z
      DOI: 10.1016/j.physd.2016.12.008
       
  • Spiral disk packings
    • Authors: Yoshikazu Yamagishi; Takamichi Sushida
      Abstract: Publication date: Available online 26 December 2016
      Source:Physica D: Nonlinear Phenomena
      Author(s): Yoshikazu Yamagishi, Takamichi Sushida
      It is shown that van Iterson’s metric for disk packings, proposed in 1907 in the study of a centric model of spiral phyllotaxis, defines a bounded distance function in the plane. This metric is also related to the bifurcation of Voronoi tilings for logarithmic spiral lattices, through the continued fraction expansion of the divergence angle. The phase diagrams of disk packings and Voronoi tilings for logarithmic spirals are dual graphs to each other. This gives a rigorous proof that van Iterson’s diagram in the centric model is connected and simply connected. It is a nonlinear analog of the duality between the phase diagrams for disk packings and Voronoi tilings on the linear lattices, having the modular group symmetry.

      PubDate: 2017-01-05T04:02:55Z
      DOI: 10.1016/j.physd.2016.12.003
       
  • Numerical bifurcation for the capillary Whitham equation
    • Authors: Filippo Remonato; Henrik Kalisch
      Abstract: Publication date: Available online 6 December 2016
      Source:Physica D: Nonlinear Phenomena
      Author(s): Filippo Remonato, Henrik Kalisch
      The so-called Whitham equation arises in the modeling of free surface water waves, and combines a generic nonlinear quadratic term with the exact linear dispersion relation for gravity waves on the free surface of a fluid with finite depth. In this work, the effect of incorporating capillarity into the Whitham equation is in focus. The capillary Whitham equation is a nonlocal equation similar to the usual Whitham equation, but containing an additional term with a coefficient depending on the Bond number which measures the relative strength of capillary and gravity effects on the wave motion. A spectral collocation scheme for computing approximations to periodic traveling waves for the capillary Whitham equation is put forward. Numerical approximations of periodic traveling waves are computed using a bifurcation approach, and a number of bifurcation curves are found. Our analysis uncovers a rich structure of bifurcation patterns, including subharmonic bifurcations, as well as connecting and crossing branches. Indeed, for some values of the Bond number, the bifurcation diagram features distinct branches of solutions which intersect at a secondary bifurcation point. The same branches may also cross without connecting, and some bifurcation curves feature self-crossings without self-connections.

      PubDate: 2016-12-11T02:34:16Z
      DOI: 10.1016/j.physd.2016.11.003
       
  • One- and two-dimensional bright solitons in inhomogeneous defocusing
           nonlinearities with an antisymmetric periodic gain and loss
    • Authors: Dengchu Guo; Jing Xiao; Linlin Gu; Hongzhen Jin; Liangwei Dong
      Abstract: Publication date: Available online 2 December 2016
      Source:Physica D: Nonlinear Phenomena
      Author(s): Dengchu Guo, Jing Xiao, Linlin Gu, Hongzhen Jin, Liangwei Dong
      We address that various branches of bright solitons exist in a spatially inhomogeneous defocusing nonlinearity with an imprinted antisymmetric periodic gain-loss profile. The spectra of such systems with a purely imaginary potential never become complex and thus the parity-time symmetry is unbreakable. The mergence between pairs of soliton branches occurs at a critical gain-loss strength, above which no soliton solutions can be found. Intriguingly, which pair of soliton branches will merge together can be changed by varying the modulation frequency of gain and loss. Most branches of one-dimensional solitons are stable in wide parameter regions. We also provide the first example of two-dimensional bright solitons with unbreakable parity-time symmetry.

      PubDate: 2016-12-04T02:03:09Z
      DOI: 10.1016/j.physd.2016.11.005
       
  • Excitability, mixed-mode oscillations and transition to chaos in a
           stochastic ice ages model
    • Authors: D.V. Alexandrov; I.A. Bashkirtseva; L.B. Ryashko
      Abstract: Publication date: Available online 30 November 2016
      Source:Physica D: Nonlinear Phenomena
      Author(s): D.V. Alexandrov, I.A. Bashkirtseva, L.B. Ryashko
      Motivated by an important geophysical significance, we consider the influence of stochastic forcing on a simple three-dimensional climate model previously derived by Saltzman and Sutera. A nonlinear dynamical system governing three physical variables, the bulk ocean temperature, continental and marine ice masses, is analyzed in deterministic and stochastic cases. It is shown that the attractor of deterministic model is either a stable equilibrium or a limit cycle. We demonstrate that the process of continental ice melting occurs with a noise-dependent time delay as compared with marine ice melting. The paleoclimate cyclicity which is near 100 ky in a wide range of model parameters abruptly increases in the vicinity of a bifurcation point and depends on the noise intensity. In a zone of stable equilibria, the 3D climate model under consideration is extremely excitable. Even for a weak random noise, the stochastic trajectories demonstrate a transition from small- to large-amplitude stochastic oscillations (SLASO). In a zone of stable cycles, SLASO transitions are analyzed too. We show that such stochastic transitions play an important role in the formation of a mixed-mode paleoclimate scenario. This mixed-mode dynamics with the intermittency of large- and small-amplitude stochastic oscillations and coherence resonance are investigated via analysis of interspike intervals. A tendency of dynamic paleoclimate to abrupt and rapid glaciations and deglaciations as well as its transition from order to chaos with increasing noise are shown.

      PubDate: 2016-12-04T02:03:09Z
      DOI: 10.1016/j.physd.2016.11.007
       
  • Spatiotemporal control to eliminate cardiac alternans using isostable
           reduction
    • Authors: Dan Wilson; Jeff Moehlis
      Abstract: Publication date: Available online 16 November 2016
      Source:Physica D: Nonlinear Phenomena
      Author(s): Dan Wilson, Jeff Moehlis
      Cardiac alternans, an arrhythmia characterized by a beat-to-beat alternation of cardiac action potential durations, is widely believed to facilitate the transition from normal cardiac function to ventricular fibrillation and sudden cardiac death. Alternans arises due to an instability of a healthy period-1 rhythm, and most dynamical control strategies either require extensive knowledge of the cardiac system, making experimental validation difficult, or are model independent and sacrifice important information about the specific system under study. Isostable reduction provides an alternative approach, in which the response of a system to external perturbations can be used to reduce the complexity of a cardiac system, making it easier to work with from an analytical perspective while retaining many of its important features. Here, we use isostable reduction strategies to reduce the complexity of partial differential equation models of cardiac systems in order to develop energy optimal strategies for the elimination of alternans. Resulting control strategies require significantly less energy to terminate alternans than comparable strategies and do not require continuous state feedback.

      PubDate: 2016-11-20T14:57:33Z
      DOI: 10.1016/j.physd.2016.11.001
       
  • Macroscopic heat transport equations and heat waves in nonequilibrium
           states
    • Authors: Yangyu Guo; David Jou; Moran Wang
      Abstract: Publication date: Available online 16 November 2016
      Source:Physica D: Nonlinear Phenomena
      Author(s): Yangyu Guo, David Jou, Moran Wang
      Heat transport may behave as wave propagation when the time scale of processes decreases to be comparable to or smaller than the relaxation time of heat carriers. In this work, a generalized heat transport equation including nonlinear, nonlocal and relaxation terms is proposed, which sums up the Cattaneo-Vernotte, dual-phase-lag and phonon hydrodynamic models as special cases. In the frame of this equation, the heat wave propagations are investigated systematically in nonequilibrium steady states, which were usually studied around equilibrium states. The phase (or front) speed of heat waves is obtained through a perturbation solution to the heat differential equation, and found to be intimately related to the nonlinear and nonlocal terms. Thus, potential heat wave experiments in nonequilibrium states are devised to measure the coefficients in the generalized equation, which may throw light on understanding the physical mechanisms and macroscopic modeling of nanoscale heat transport.

      PubDate: 2016-11-20T14:57:33Z
      DOI: 10.1016/j.physd.2016.10.005
       
 
 
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